8000 Match up array coercion for rust-lang/rust#140283 by Veykril · Pull Request #19911 · rust-lang/rust-analyzer · GitHub
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Match up array coercion for rust-lang/rust#140283 #19911

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Match up array coercion for rust-lang/rust#140283 #19911

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4 changes: 3 additions & 1 deletion crates/hir-ty/src/infer/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1164,7 +1164,9 @@ impl InferenceContext<'_> {
expected: &Expectation,
) -> chalk_ir::Ty<Interner> {
let elem_ty = match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
// Avoid using a type variable as the coerce_to type, as it may resolve
// during the first coercion instead of being based on the common type.
Some(TyKind::Array(st, _) | TyKind::Slice(st)) if !st.is_ty_var() => st.clone(),
_ => self.table.new_type_var(),
};

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36 changes: 34 additions & 2 deletions crates/hir-ty/src/tests/coercion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,7 @@ fn foo<T>(x: &[T]) -> &[T] { x }
fn test() {
let x = if true {
foo(&[1])
// ^^^^ adjustments: Deref(None), Borrow(Ref('?8, Not)), Pointer(Unsize)
// ^^^^ adjustments: Deref(None), Borrow(Ref('?7, Not)), Pointer(Unsize)
} else {
&[1]
};
Expand Down Expand Up @@ -148,7 +148,7 @@ fn foo<T>(x: &[T]) -> &[T] { x }
fn test(i: i32) {
let x = match i {
2 => foo(&[2]),
// ^^^^ adjustments: Deref(None), Borrow(Ref('?8, Not)), Pointer(Unsize)
// ^^^^ adjustments: Deref(None), Borrow(Ref('?7, Not)), Pointer(Unsize)
1 => &[1],
_ => &[3],
};
Expand Down Expand Up @@ -957,3 +957,35 @@ fn f() {
"#,
);
}

#[test]
fn coerce_array_elements() {
check_no_mismatches(
r#"
// Check that least upper bound coercions don't resolve type variable merely based on the first
// coercion. Check issue rust-lang/rust#136420.

fn foo() {}
fn bar() {}

fn infer<T>(_: T) {}

fn infer_array_element<T>(_: [T; 2]) {}

fn main() {
infer(if false {
foo
} else {
bar
});

infer(match false {
true => foo,
false => bar,
});

infer_array_element([foo, bar]);
}
"#,
);
}
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